Hydraulic shock absorbers



Inventor A. R. A. DAY

HYDRAULIC SHOCK ABSORBERS Filed July 24. 1959 Feb. 13, Y1962 UnitedStates Patent 3,020,981 HYDRAULIC SHOCK ABSORBERS Alan Robert AndrewDay, York, England, assigner to Armstrong Patents Co. Limited, Beverley,England Filed July 24, 1959, ser. No. 829,382 Claims priority,application Great Britain Aug. 1, 1958 2 Claims. (Cl. 18S- 160) Thisinvention relates to hydraulic shock absorbers of the type wherein apiston is displaceable in a hydraulic pressure cylinder responsive tomotion of a sprung mass such as a vehicle body, and wherein the pressurecylinder is adapted to communicate with a hydraulic reservoir betweenwhich and said pressure cylinder a hydraulic damping medium e.g. oil,flows due to motion of the piston.

In a shock absorber of the type described, it is not possible completelyto ll the reservoir with hydraulic damping medium due inter alia to thedifferential displacement of hydraulic medium from the pressure cylinderas the piston rod is introduced therein to various extents. Therefore itis conventional practice in such a reservoir to provide an air space. inone type of shock absorber, the hydraulic medium and air are storedtogether in the reservoir. Displacement of the piston in the pressurecylinder causes heating of the hydraulic medium due to passage of themedium through damping valves, but as the hydraulic medium comes intointimate contact with the outer walls of the reservoir, which areusually of thin metals, the excess heat can readily be dissipated intothe atmosphere through the reservoir walls. However, as the hydraulicmedium is also in intimate contact with the air in the reservoir,aeration of the hydraulic medium occurs when the shock absorber isshaken owing to movement of the vehicle within which it is mounted and aloss of eiciency results. Thus, the advantage gained by easy cooling ofthe hydraulic medium via the reservoir walls is, to a considerableextent, lost because o-f the hydraulic medium becoming aerated.

Aeration of the oil can be prevented by using a ilexible diaphragm toseparate the air in the reservoir tube from the hydraulic medium.However, the exible diaphragm usually acts as a heat insulator, forexample if made of rubber, and hence the hydraulic medium is separatedfrom the walls of the reservoir by a heat insulating diaphragm and alayer of air. The result is that rapid dissipation of heat from thehydraulic medium to the atmosphere is effectively prevented.

It is an object of the invention to avoid or mitigate against thesedisadvantages in a shock absorber employing a flexible diaphragm.

According to the present yinvention a shock absorber of the typedescribed incorporates a ilexible diaphragm arranged to divide thereservoir space of the shock absorber into two separate chambers in sucha way that the extent of the diaphragm is limited to a predeterminedportion of the reservoir, hydraulic medium discharged from the pressurecylinder being passed directly into one of said chambers and the otherchamber being vented to atmosphere.

The flexible diaphragm `is preferably arranged to surround the intakeend of the pressure cylinder.

Conveniently the iiexible diaphragm may be arranged coaxially with andexternally of the pressure cylinder to embrace a predetermined portionof the same, including the intake end of said pressure cylinder.

In one especially advantageous application of the invention, wherein thepressure cylinder is Surrounded by a tubular member arranged coaxiallywith the pressure cylinder, and the reservoir space is defined betweensaid pressure cylinder and said tubular member, one end of the ilexiblediaphragm encloses the intake end of the 3,020,981 Patented Feb. 13,1962 ICC pressure cylinder and the other end of said iiexible diaphragmis seated tightly against the inner wall of the tubular member at laposition spaced apart from the discharge end of the pressure cylinder,the llexible diaphragm thus having a somewhat elongated coniiguration.

Preferably the pressure cylinder is arranged to discharge hydraulicmedium into direct contact with the tubular member.

The invention will be described further by way of exampie and withreference to the accompanying drawings in which:

FIG. l is a sectional elevation of a tubular telescopic shock absorberembodying the invention,

FIG. 2 is a fragmentary sectional elevation illustrating a modificationof the shock absorber of FIG. 1, and

FIG. 3 is a fragmentary sectional elevation illustrating a furthermodification of lthe shock absorber of FIG. 1.

In the shock absorber shown in FIG. 1 Ia piston 10 carried on la pistonrod 12 is arranged for reciprocation in a metal pressure cylinder 14,the piston rod 12 passing out of one end of the cylinder through a head16 incorporating a pressure oil seal 18. The head 16 is mounted within ametal outer tubular member 20 arranged coaxially With the pressurecylinder 14 and defining therewith an annular space constituting areservoir space for hydraulic damping medium such as oil. e

The end of the pressure cylinder remote from the head 16 is closed bythe base member 22 formed with a bore 24 controlled by a spring loadedplate valve 26. The base member 22 carries a dished cup member 28between which and the corresponding end of the tubular member 20 istightly gripped one end of a flexible diaphragm 30, the latter beingformed with an internal bead 32 adapted to co-operate with a recessedportion 34 of the cup member 28 to ensure a proper seating of theiiexible diaphragm 30 against the end of the member 20.

The exible diaphragm will be seen to be of elongated congurationextending through the reservoir space so as to embrace the pressurecylinder 14 in spaced relation thereto. It will be noted that the baseend of the pressure cylinder is effectively enclosed by a correspondingend of the flexible diaphragm. Within a slightly recessed region of theopposite end of the flexible diaphragm there is engaged a rigid collar36, the arrangement of which is such that when the several parts of theshock absorber above described are assembled together, the tubularmember 20 may be subjected to a swaging operation to reduce its diameterand securely -grip the said end of the flexible diaphragm inco-operation with the collar 36.

The self-centering plate valve 42 takes the form of an annular plateslideably mounted upon a spindle 39 one end of which is mounted withinthe tube 40. The other end of the spindle 39 is threaded and carries anut 41 between which and the plate 42 is disposed a coiled spring 43arranged concentrically with the spindle 39. The spring 43 is held in astate of compression between the nut 41 and the spindle 39 and serves tohold the plate 42 in closing contact with the lower end of the tube 40'in the absence of superior opposing iiuid pressure within the tube 40.The pressure exerted by spring 43 upon the plate 42 may be adjusted byadjusting the position of nut'41 upon the spindle 39. The head 16 of theshock absorber further includes an oblique bore 38 communicating with adischarge tube 40, the lower end of which is closed by a self-centeringplate valve 42, the oblique bore 38 communicating with the interior ofthe pressure cylinder 14 above the piston 10. The piston 10 is itselfprovided with a bore 11 allowing liquid flow through the piston, and thebore 11 is controlled by a spring loaded plate valve 13.

In the operation of the shock absorber described herein, the piston rod12 is adapted to be connected as by an eye 44 to one part of a vehicleand the tubular member 2li and pressure cylinder 14 are similarlyadapted, as by means of threaded studs 46 and rubber blocks 48 to beconnected to another part of a vehicle. Vehicle riding movements suchthat the piston is caused to be slightly withdrawn from the pressurecylinder 14 thus cause hydraulic damping medium in that cylinder andabove the piston 10 to ilow through the oblique bore 38, discharge tube40 and valve 42 into the space between the pressure cylinder 14 andflexible diaphragm 30, this space thus constituting a reservoir chamber.At the same time, since such movement of the piston 10 causes the platevalve 13 to remain closed, hydraulic damping medium is drawn into thepart of the pressure chamber 14 below the piston via plate valve 26 i.e.from the reservoir chamber. ln the opposite direction of movement of thepiston, the plate valve 26 remains closed but the plate valve 13 opensand therefore hydraulic damping medium is allowed to flow through thebore 11 in the piston, from one side thereof to the other. During thistime however there is differential displacement of the hydraulic dampingmedium from the portion of the pressure cylinder 14 above the piston 10due to the introduction or the piston rod 12, and hydraulic dampingmedium displaced in this way again llows to the reservoir chamberthrough the bore 38 and discharge tube 40.

Thus there is cyclic flow of hydraulic damping medium in one directiononly through the shock absorber, and the flexible diaphragm 30 yieldsand expands as this cyclic tlow takes place to allow for the varyingvolume of hydraulic damping medium contained in the reservoir space.However, it will be noted that the tlexible diaphragm 30 does not definewith the tubular member 20, a totally cnclosed air chamber but that themember is provided with a vent hole 21 whereby the air surrounding theflexible diaphragm is always at atmospheric pressure. In this way therise in temperature normally associated with a totally enclosed airchamber is avoided and the deleterious effects of high temperature onthe flexible diaphragm are largely eliminated. A further advantage ofthe invention resides in the fact that since the air in the air chamberis not subjected to compression, this in turn relieves pressure from theoil seal 18.

It will be noted that the collar 36 holds the upper end of the diaphragmin fluid-tight contact with the inner surface of the metal outer tubularmember 20 at a position spaced from the upper end of the pressurecylinder, thus enabling the hydraulic damping medium to come into directcontact with the wall of tubular member 20 so that excess heat possessedby the hydraulic medium may be rapidly dissipated to the atmospherethrough the metal wall of tubular member 20. Moreover the heating of thehydraulic medium occurs due to its passage through the valves in theshock absorber, particularly the valve 42 of the discharge tube 40.Hydraulic medium leaving the discharge tube via the valve 42 spraysdirectly onto the metal wall of the tubular member 20, thus achievingrapid cooling.

The head 16 is formed beneath the seal 18 with an annular chamber 50from which extends a port 52 leading to a drain tube 54, the latterbeing of suflicient length to ensure that any oil draining therefromwill enter directly into the main body of hydraulic medium. It will beappreciated that the discharge tube 40 is also of a length such thathydraulic medium expelled therefrom will likewise enter directly intothe main body of hydraulic medium in the reservoir chamber.

It will be appreciated that other methods may be used to secure theflexible diaphragm 30 to the cup member 28. Thus, in the construction ofFIG. 2, the end of the diaphragm 30 is gripped between the outer surfaceof the cup member 28 and the inner surface of a metal band 29,concentric with the cup member, the cup member and the metal band beingstepped or flanged to provide abutments for a bead 31 at the end of thediaphragm 30 whereby an adequate grip between the diaphragm and the cupmember is obtained. Alternatively, as shown in FIG. 3, the end of thediaphragm 30 may be bonded to the inner surface of the cup member 28. InFIGS. 1, 2 and 3, like numbers refer to like parts.

The shock absorber of the present invention combines means forseparating the hydraulic damping medium and air with means for rapidlycooling the hydraulic damping medium by providing a ilexible separatordiaphragm which extends over alimited portion of the length of the outertubular member, and thus allowing the hydraulic medium to come intodirect contact with the tubular member over a portion of its length.

I claim:

1. A hydraulic shock absorber comprising a pressure cylinder, a pistondisplaceable in said pressure cylinder, a tubular vessel surrounding thepressure cylinder and arranged coaxially with the pressure cylinder, acylinder head arranged to close one end of the pressure cylinder and thetubular vessel, said cylinder head having a passage connecting thepressure cylinder with the tubular vessel, a discharge tube extendinginto the tubular vessel from said passage, a frusto-conical flexiblediaphragm, a rigid collar having an external diameter smaller than theinternal diameter of said tubular vessel and larger than the internaldiameter of the large end of said frustoconical flexible diaphragm, saidcollar being adapted to frictionally hold and seal said large end ofsaid flexible diaphragm against said tubular vessel and below thedischarge end of said discharge tube, an annular bead formed on theother end of said frusto-conical flexible diaphragm, a dished cup memberhaving an annular recess complementary to and receiving said bead forsecuring the small end of said frusto-conical flexible diaphragm to anend of said tubular vessel, the wall of the tubular vessel being boredon the side of the diaphragm remote from the pressure cylinder.

2. A hydraulic shock absorber as defined in claim 1 wherein the internaldiameter of said rigid collar is substantially larger than the externaldiameter of said pressure cylinder and forms therewith an annularpassage to allow unobstructed flow of hydraulic medium.

References Cited in the file of this patent UNITED STATES PATENTS

